Complex Passwords Not Allowed on User Creation

Creating a new user from the panel with a complex password seems to cause a validation error.

The first password I tried was simple Abc123 - which was acceptable
The second password I tried was Abc!123 - which wouldn't be accepted

When updating the password via "Edit Profile" to Abc!123 - this works fine, which means it's only to do with password creation from the New User page, which could cause issues for customers signing up (lets say through WHMCS) who create complex passwords with special characters.